Bifunctional precursors for the preparation of liquid crystals

ABSTRACT

Bifunctional compounds of the formula (I), ##STR1## in which: ##STR2## are naphthalene-2,6-diyl or ##STR3## is naphthalene-2,6-diyl or ##STR4## U, X, Y and Z are --CH═, --CF═ and --N═, with the proviso that --CF═ and --N═ may each only be represented at most twice per six-membered ring, and that --CF═ and --N═ may not at the same time be represented twice in a six-membered ring; 
     Hal is Cl, Br or I; or H, if X and/or Y are --CF═ 
     R 3  is CH 3  or OCH 3   
     l is 0 or 1 
     m and n are 0, 1, 2 or 3. 
     The compounds of the formula I are useful intermediates for the preparation of liquid-crystalline mixtures.

BACKGROUND OF THE INVENTION

The unusual combination of anisotropic and fluid behavior of liquid crystals has resulted in their use in electro-optical switching and display devices, where their electrical, magnetic, elastic and/or thermal properties can be utilized to cause changes in alignment. Optical effects can be achieved, for example, with the aid of biorefringence, the inclusion of dichroically absorbing dyes ("guest-host mode") or light scattering.

In order to satisfy the constantly increasing practical requirements in the various areas of application, there is a constant demand for new improved liquid-crystal mixtures and thus also for a large number of mesogenic compounds of various structures. This applies both to applications in which nematic liquid-crystal phases are used, and to those having smectic liquid-crystal phases.

The processes for the preparation of the components of such liquid-crystal mixtures also have to meet constantly increasing requirements, in particular with respect to the effects on ecology, but also with respect to process economy. The liquid-crystal mixtures virtually always comprise at least two different classes of substance, and very frequently at least two homologs differing, for example, in the chain length of an alkyl or alkoxy substituent are very frequently found in a certain class of substances (see, for example, EP-A 497 176, U.S. Pat. No. 5,026,506, EP-A 495 686, EP-A 319 167, EP-B 317 587, EP-A 316 181, EP-A-315 958).

Attempts have therefore already been made to find ways in which the syntheses of various classes of substance, but ones which contain common part-structures, can be accomplished on the basis of the same precursors.

EP-A 354 434 describes derivatives of boric acid, including boronic acids, which are reacted with certain halogen compounds with catalysis with metal compounds to give liquid-crystal compounds.

However, a significant disadvantage of the compounds described in EP-A 354 434, which impairs inexpensive production and is ecologically unacceptable due to additional processing steps, is the fact that on further conversion into liquid-crystal compounds for the preparation of more than one homolog of a substance class, in each case more than one boric acid derivative or halogen compound is necessary, since the substitution pattern of the desired target molecules is already defined in the starting compounds for the boric acid derivatives or hydrogen compounds, and homologization is no longer possible in the subsequent reaction steps.

For the preparation of different classes of substance--which is taken to mean here, for example, not only phenylpyridine versus phenylpyrimidine, but also, for example, 5-alkyl- versus 5-alkoxy- versus 5-alkoxycarbonyl- versus 5-alkylcarbonyloxypyrimidine, since significant differences with respect to mesogenic properties, stability, synthesis and thus not least also of the precursors exist--different precursors must in each case be prepared in accordance with the prior art.

DETAILED DESCRIPTION OF THE INVENTION

The disadvantages described are overcome by the novel bifunctional compounds of the formula (I), ##STR5## in which: ##STR6## are naphthalene-2,6-diyl or ##STR7## is naphthalene-2,6-diyl or ##STR8##

U, X, Y and Z are --CH═, --CF═ and --N═, with the proviso that --CF═ and --N═ may each only be represented at most twice per six-membered ring, and that --CF═ and --N═ may not at the same time be represented twice in a six-membered ring;

Hal is Cl, Br or I; or H, if X and/or Y are --CF═

R³ is CH₃ or OCH₃

l is 0 or 1

m and n are 0, 1, 2 or 3.

Preference is given to compounds in which

l=0

at least one of U, X, Y and Z is --N═ and at most one is --CF═, and the others are --CH═

m is 0, 1 or 2

n is 0, 1 or 2

R³ is CH₃ or OCH₃

Hal is Br or I.

Particular preference is given to compounds in which

l═0

one or two of U, X, Y and Z is --N═, and the others are --CH═

m is 0, 1, 2 or 3

n is 0

Hal is Br or I.

Very particular preference is given to compounds in which

l=0

one or two of U, X, Y and Z is --N═, and the others are --CH═

m and n are 0

Hal is Br.

Particular preference is given to the compounds 1a-c. ##STR9##

The novel compounds can be successively and selectively derivatized via their two different functionalities--the halogen and benzyl ether functions.

Thus, they can be reacted via the halogen function by metal-catalyzed processes, as described, for example, in DE-C 3 930 663 and EP-A 354 434, with boronic acids of Formula II ##STR10## in which R⁴ ═H, alkyl having 1 to 18 carbon atoms, in which, in addition, one or more nonadjacent --CH₂ -groups can be replaced by --O--, --C(O)--, --CH═CH--, --OC(O)-- and --Si(CH₃)₂ --, and ##STR11## is 1,4-phenylene, optionally substituted once, twice or three times by F, to give intermediates of the formula (III) ##STR12## in which the symbols are as defined in (I) and (II).

Preference is given to the conversion, for example into compounds of the formula (III), by a process proposed in the German Patent Application P 42 36 103.6 with the title "Process for cross-coupling aromatic boronic acids with aromatic halogen compounds or perfluoroalkylsulfonates", in which the novel compound is coupled to aromatic halogen compounds or perfluoroalkylsulfonates in the presence of a base and catalytic amounts of metallic palladium, optionally on a support material, which comprises adding a base and catalytic amounts of a ligand to the reaction mixture.

It is furthermore possible to react the novel compounds of the formula I by metal-catalyzed processes, as described, for example, in DE-C 3 930 663 and EP-A 354 434, with alkyl organometallic compounds to give intermediates of the formula (IV) ##STR13## in which R⁵ is alkyl having 1 to 18 carbon atoms, in which, in addition, one or more non-adjacent --CH₂ -- groups can be replaced by --O--, --CH═CH-- or --Si(CH₃)₂ --, where --O-- must not be bonded directly to the ring,

and the other symbols are as defined in the formula (I).

In addition, it is possible to convert the halogen functions in the compounds of the formula (I) into an OH group by reaction with OH nucleophiles.

Novel compounds of the formula V ##STR14## in which the symbols are as defined in the formula (I), with the proviso that in ##STR15## at least U and/or Z are --N═ and X and/or Y must not be --N═, are preferably reacted by a process proposed in the German Patent Application P 42 36 102.8 with the title, "Process for the preparation of hydroxyheteroaromatic compounds", with a metal hydroxide in a solvent under atmospheric pressure using catalytic amounts of sulphur to give compounds of the formula VI ##STR16## in which the symbols are as defined in formula (V).

These intermediates (VI) can be converted by standard methods of synthesis for alkyl aryl ethers or aryl alkanoates, into intermediates of the formula (VII) ##STR17## in which R⁶ is alkyl having 1 to 18 carbon atoms, in which, in addition, one or more non-adjacent --CH₂ -- groups can be replaced by --O--, --C(═O)--, --CH═CH-- or --Si(CH₃)₂ --,

and the other symbols are as defined in the formula (V).

Furthermore, intermediates of the formula (VI) can be converted, by standard methods by reaction with carboxylic acids or carboxylic acid derivatives (for example halides or anhydrides), into intermediates of the formula (VIII) ##STR18## in which R⁷ is alkyl having 1 to 18 carbon atoms, in which, in addition, one or more non-adjacent --CH₂ -- groups can be replaced by --O--, --CH═CH-- or --Si(CH₃)₂ --, ##STR19## is 1,4-phenylene, optionally substituted once, twice or three times by F, or 1,4-cyclohexylene or 1,3-dioxane-2,5-diyl.

The intermediates (III), (IV), (VI), (VII) and (VIII) are likewise the subject-matter of the present invention.

Removal of the benzyl ether function in the intermediates (I), (III), (IV), (VII) and (VIII) by standard methods (for example described in T. W. Greene, P. G. W. Wuts, Protective Groups in Organic Synthesis, J. Wiley & Sons, New York, 1991, pp. 156-160) gives novel intermediates containing a phenolic OH function, which are likewise the subject-matter of the present invention: ##STR20##

These phenolic compounds of the formulae (IX) to (XIII) can be converted, by standard methods, into numerous types of components for liquid-crystal mixtures. For example, reaction with alkyl halides or equiavlent alkylating agents gives aryl alkyl ethers of the formula (XIV) ##STR21## in which the symbols are as defined in the formula (III).

Analogous reactions can be carried out with (XI), (XII) and (XIII).

Furthermore, reaction with carboxylic acids or carboxylic acid derivatives (for example halides or anhydrides) gives aryl carboxylates, for example (XV) from (XI) ##STR22## in which the symbols are as defined in the formulae (I) and (VIII), and p can be zero or one or two. Analogous reactions can be carried out with (X), (XII) and (XIII).

Furthermore, reaction of perfluoroalkanesulfonic acid derivatives with (IX), (X), (XI), (XII) or (XIII) gives perfluoroalkanesulfonic acid ester intermediates, which are coupled with boronic acids with metal catalysis by standard methods, as described, for example, in DE-C 3 930 663, EP-A 354 434 and German Patent Application P 42 36 103.6 with the title "Process for the cross-coupling of aromatic boronic acids with aromatic halogen compounds or perfluoroalkylsulfonates", to give components of liquid crystals of the formulae (XVI to XIX): ##STR23## in which ##STR24## is 1,4-phenylene, which may also carry 1, 2 or 3 F substituents, or is pyridine-2,5-diyl or naphthalene-2,6-diyl.

Novel compounds of the formula (I) can preferably be used in one of the ways described above for the preparation of components of liquid crystals of the formula (XX) ##STR25## in which r is 0, 1, 2 or 3, and

r⁴ is as defined in the formula (II).

The compounds (I) can particularly advantageously be prepared by coupling an arylboronic acid of formula (XXI), as proposed in German Patent Application P 42 36 105.2 with the title "Arylboronic acids as precursors for the preparation of components of liquid crystals": ##STR26## in which the substituents and indices have the following meanings: ##STR27## is naphthalene-2,6-diyl or ##STR28## R is CH₃ or OCH₃ m is 0, 1, 2 or 3

n is 0, 1 or 2

by known processes (for example EP-A 354 434 or as proposed in German Patent Application P 42 36 103.6 with the title "Process for the cross-coupling of aromatic-boronic acids with aromatic halides or perfluoroalkylsulfonates"), with a halide of the formula (XXII): ##STR29## in which the symbols are as defined in the formula (I), and

Hal' is Cl, Br, I or perfluoroalkanesulfonate.

Preference is given to ##STR30##

They are either commercially available, for example (XXIIa; m═0), (XXIId), (XXIIg) or can be obtained by standard methods from known or commercially available materials: for example (XXIIb, m═0) by reacting commercial 4-bromo-4'-hydroxybiphenyl with perfluroalkanesulfonic acid derivatives; for example (XXIIc) by reacting commercial 6-bromo-2-hydroxynaphthalene with perfluoroalkanesulfonic acid derivatives; (XXIIe) as described in J. Chem. Soc. (C) 1971, 1889, (XXIIm) analogously to Z. Chem. 17, 333 (1977); (XXIII) by reacting 2-(4-halophenyl)-5-hydroxypyrazine--prepared analogously to H. Heberer, Degree Thesis Halle, 1967, cited in "Flussige Kristalle in Tabellen" Liquid crystals in tables!, ed. D. Demus, VEB Verlag fur Grundstoffindustrie, Leipzig 1974, p. 265--with, for example, phosphorus halides or perfluoroalkanesulfonic acid derivatives; (XXIIk) analogously to (XXIII), but using 5-(4-halophenyl)-2-hydroxypyridine, prepared analogously to Z. Chem. 18, 403 (1978); (XXIIi) analogously to (XXIII), but using 5-(4-halophenyl)-2-hydroxypyrimidine, prepared analogously to J. Prakt. Chem. 501, 169 (1979); (XXIIh) analogously to Mol. Cryst. Liq. Cryst. 42, 1225 (1977); (XXIIf) as described in J. Am. Chem. Soc. 71, 2798 (1949); (XXIIj) analogously to "Adv. in Liquid Crystal Research and Application" (ed. L. Bata), Oxford, Pergamon Press, Budapest.

The novel compounds are versatile units for the synthesis of polycyclic aromatic compounds which can be employed in many areas of organic chemistry, for example for the preparation of components for the liquid-crystal mixtures, pharmaceuticals, cosmetics or crop-protection agents.

They are preferably used as intermediates for the preparation of components for liquid-crystal mixtures, in particular ferroelectric mixtures. Such components are described, for example, in EP-A 354 434, EP-A 307 880, EP-B 283 506, EP-B 357 702 and EP-A 439.089.

Use of the novel compounds of the formula (I) allows synthetic steps to be saved in the preparation of components for liquid-crystal mixtures, which brings enormous advantages, in particular, in large-scale industrial synthesis. The invention allows the provision of a broad product range from a single intermediate, which greatly simplifies the process from a technical, economic and ecological point of view.

A comparison of schemes 1A--for a process using compounds as per EP-A 354 434--and 1B--for a process using the novel compounds--shows that a total of 8 synthetic steps are necessary for the synthesis of 2 homologous phenylpyrimidines by the process using the compounds of EP 354 434, but only 7 synthetic steps are required for the preparation of the same two homologs in a process using the novel compounds of the formula (I).

The advantage is even clearer for process economy and ecology if--as described, for example in EP-A 307 880, Example 34--3 homologs or--as, for example, in EP-B 283 506, Example 5--4 homologs of a substance class are to be prepared.

Scheme 2A shows a synthesis using the compounds proposed in EP-A 354 434. For the preparation of the three homologous phenyl pyrimidines, 12 synthetic steps are required if said precursors are used. Scheme 2B shows the synthesis of the same 3 homologs, but using the novel bifunctional precursor (Ib); only 8 synthetic steps are necessary. ##STR31##

The excellent suitability of the compounds (I) as universal precursors, for example for liquid crystals, is furthermore confirmed by scheme 3. EP-A 508 330 proposes a liquid-crystal compound comprising two types of phenyl pyrimidines, of which each type is represented in the mixture by 3 homologs (Table 4, Example 14):

Type A: 2-(4-alkoxyphenyl)-5-alkylpyrimidines

Type B: 2-(4-alkylbiphenyl)-4'-yl)-5-alkylpyrimidines

Scheme 3 shows that the novel compound (Ib) is suitable for the preparation of both types. This enables the preparation of a relatively large amount of (Ib), which is a significant advantage, from the point of view of both process economy and process ecology, compared with the linear synthesis of each of types A and B, which in each case takes place in small production volumes.

Scheme 4 confirms that a mixture which, besides the above phenylpyrimidine of type A, also contains two further types,

C: 5-alkoxy-2- 4-substituted phenyl!pyrimidine

D: 5-(4-substituted phenyl)-2-(4-substituted phenyl)pyrimidine

and is proposed in EP-A 469 800, Table 2, Example 9, can also be prepared in a favourable manner from the novel compound (Ib).

In their totality, schemes 1 to 4 confirm that the bifunctional precursors of the formula (I) are suitable for the preparation of a wide variety of types of liquid crystal from a single precursor. The preparation of a precursor which is universal in this way and subsequently the end products derived therefrom can be carried out significantly more economically than that of a plurality of individual precursors. ##STR32##

EXAMPLES Example 1 5-bromo-2- 4-(benzoxy)phenyl!pyrimidine ##STR33##

A solution of 104 g of 2,5-dibromopyrimidine, 100 g of 4-benzoxyphenylboronic acid, 4.75 g of Pd (10% on activated charcoal), 4.5 g of triphenylphosphene and 93 g of sodium carbonate in 1 l of toluene, 0.5 l of ethanol and 0.3 l of water is heated at 80° C. for 24 hours. After filtration, the organic phase is separated off and evaporated to dryness in vacuo. The residue is recrystallized from acetonitrile: 83 g of solids of melting point 153°-155° C.

Examples 2-37 are obtained analogously:

    ______________________________________     Example 2   5-bromo-2- (4-benzoxy-2,3-difluoro)-                 phenyl!pyrimidine     Example 3   5-bromo-2- (4-benzoxy-3-fluoro)phenyl!-                 pyrimidine     Example 4   5-bromo-2- (4-benzoxy-2-fluoro)phenyl!-                 pyrimidine     Example 5   5-chloro-2- (4-benzoxy)phenyl!pyrimidine     Example 6   5-chloro-2- 4-benzoxy-2,3-difluoro)-                 phenyl!pyrimidine     Example 7   5-chloro-2- (4-benzoxy-3-fluoro)phenyl!-                 pyrimidine     Example 8   5-chloro-2- (4-benzoxy-2-fluoro)phenyl!-                 pyrimidine     Example 9   5-iodo-2- (4-benzoxy)phenyl!pyrimidine     Example 10  5-iodo-2- (4-benzoxy-2,3-difluoro)-                 phenyl!pyrimidine     Example 11  5-iodo-2- (4-benzoxy-3-fluoro)phenyl!-                 pyrimidine     Example 12  5-iodo-2- (4-benzoxy-2-fluoro)phenyl!-                 pyrimidine;     Example 13  deleted     Example 14  5-bromo-2- 4-benzoxy)phenyl!pyridine;                 m.p. 159-160°     Example 15  5-bromo-2- (4-benzoxy-2,3-difluoro)-                 phenyl!pyridine     Example 16  5-bromo-2- (4-benzoxy-3-fluoro)phenyl!-                 pyridine     Example 17  5-bromo-2- (4-benzoxy-2-fluoro)phenyl!-                 pyridine     Example 18  5-chloro-2- 4-benzoxy)phenyl!pyridine     Example 19  5-chloro-2- (4-benzoxy-2,3-difluoro)-                 phenyl!pyridine     Example 20  5-chloro-2- (4-benzoxy-3-fluoro)-                 phenyl!pyridine     Example 21  5-chloro-2- (4-benzoxy-2-fluoro)phenyl!-                 pyridine     Example 22  5-iodo-2- (4-benzoxy)phenyl!pyridine     Example 23  5-iodo-2- (4-benzoxy-2,3-difluoro)-                 phenyl!pyridine     Example 24  5-iodo-2- (4-benzoxy-3-fluoro)phenyl!-                 pyridine     Example 25  5-iodo-2- (4-benzoxy-2-fluoro)phenyl!-                 pyridine     Example 26  5-bromo-2- 4-(benzoxy)phenyl!pyrazine     Example 27  5-bromo-2- (4-benzoxy-2,3-difluoro)-                 phenyl!pyrazine     Example 28  5-bromo-2- (4-benzoxy-3-fluoro)phenyl!-                 pyrazine     Example 29  5-bromo-2- (4-benzoxy-2-fluoro)phenyl!-                 pyrazine     Example 30  5-chloro-2- 4-(benzoxy)phenyl!pyrazine     Example 31  5-chloro-2- (4-benzoxy-2,3-difluoro)-                 phenyl!pyrazine     Example 32  5-chloro-2- (4-benzoxy-3-fluoro)phenyl!-                 pyrazine     Example 33  5-chloro-2- (4-benzoxy-2-fluoro)-                 phenyl!pyrazine     Example 34  5-iodo-2- 4-(benzoxy)phenyl!pyrazine     Example 35  5-iodo-2- 4-benzoxy-2,3-difluor)phenyl!-                 pyrazine     Example 36  5-iodo-2- (4-benzoxy-3-fluoro)phenyl!-                 pyrazine     Example 37  5-iodo-2- (4-benzoxy-3-fluoro)phenyl!-                 pyrazine     Example 38  5-bromo-2- 5-benzoxypyridin-2-yl!-                 pyrimidine     Example 38 a                 6-bromo-3-(4-benzoxy)phenylpyridazine     Example 38 b                 6-chloro-3-(4-benzoxy)phenylpyridazine;                 m.p. 186-189° C.     Example 38 c                 6-iodo-3-(4-benzoxy)phenylpyridazine     ______________________________________

Example 39 ##STR34##

A solution of 3.87 g of 5-bromo-2-chloropyrimidine, 4.56 g of 4-benzoxyphenylphenylboronic acid, 0.24 g of tetrakis(triphenylphosphene)palladium(0) and 4.2 g of sodium carbonate in 45 ml of toluene, 22 ml of ethanol and 15 ml of water is heated at the boil for 2 hours. Work-up as in Example 1 and purification by chromatography (SiO₂ /CH₂ Cl₂) gives 4.1 g of colorless solid of melting point 158°-160° C.

Examples 40-54 are obtained analogously:

    ______________________________________     Example 40  2-chloro-5- (4-benzoxy-2,3-difluoro)-                 phenyl!pyrimidine     Example 41  2-chloro-5- (4-benzoxy-3-fluoro)phenyl!-                 pyrimidine     Example 42  2-chloro-5- (4-benzoxy-2-fluoro)phenyl!-                 pyrimidine     Example 43  2-bromo-5- (4-benzoxy-2,3-difluoro)-                 phenyl!pyrimidine     Example 44  2-bromo-5- (4-benzoxy-2,3-difluoro)-                 phenyl!pyrimidine     Example 45  2-bromo-5- (4-benzoxy-3-fluoro)phenyl!-                 pyrimidine     Example 46  2-bromo-5- (4-benzoxy-2-fluoro)phenyl!-                 pyrimidine     Example 47  2-bromo-5- (4-benzoxy)phenyl!pyridine     Example 48  2-bromo-5- (4-benzoxy-2,3-difluoro)-                 phenyl!pyridine     Example 49  2-bromo-5- (4-benzoxy-3-fluoro)phenyl!-                 pyridine     Example 50  2-bromo-5- (4-benzoxy-2-fluoro)phenyl!-                 pyridine     Example 51  2-chloro-5- (4-benzoxy)phenyl!pyridine     Example 52  2-chloro-5- (4-benzoxy-2,3-difluoro)-                 phenyl!pyridine     Example 53  2-chloro-5- (4-benzoxy-3-fluoro)phenyl!-                 pyridine     Example 54  2-chloro-5- (4-benzoxy-2-fluoro)phenyl!-                 pyridine     ______________________________________

Example 55 ##STR35##

A solution of 17.6 g of 2-bromo-6-fluoropyridine (preparation as described in DE-A 4 040 575), 22.8 g of 4-benzoxyphenylboronic acid and 21.2 g of sodium carbonate in 300 ml of toluene, 150 ml of ethanol and 100 ml of water is refluxed for 2 hours in the presence of tetrakis(triphenylphosphene)palladium (0). The organic phase is separated off and evaporated to dryness in vacuo: 31 g of crude product; recrystallization from 220 ml of acetonitrile gives 20.8 g of product.

Examples 56-58 are obtained analogously:

    ______________________________________     Example 56  6-fluoro-3- (4-benzoxy-2,3-difluoro)-                 phenyl!pyridine     Example 57  6-fluoro-2- (4-benzoxy-3-fluoro)phenyl!-                 pyridine     Example 58  6-fluoro-2- (4-benzoxy-2-fluoro)phenyl!-                 pyridine     ______________________________________

Example 59 ##STR36##

A solution of 37.2 g of 4-bromophenyl trifluoromethanesulfonate, 34.2 g of 4-benzoxyphenylboronic acid, 1.8 g of tetrakis(triphenylphosphene)palladium (0) and 50 g of sodium carbonate in 450 ml of toluene, 225 ml of ethanol and 150 ml of water is refluxed for 12 hours. Work-up as in Example 1 and recrystallization of acetonitrile gives 34.2 g of colorless crystals at melting point 157°-158° C.

Examples 60-127 are obtained analogously:

    ______________________________________     Example 60  4-bromo-4'-benzoxy-2',3'-difluorobiphenyl     Example 61  4-bromo-4'-benzoxy-2'-fluorobiphenyl     Example 62  4-bromo-4'-benzoxy-3'fluorobiphenyl     Example 63  4-bromo-3-fluoro-4'-benzoxybiphenyl     Example 64  4-bromo-3-fluoro-4'-benzoxy-2',3'-                 difluorobiphenyl     Example 65  4-bromo-3-fluoro-4'-benzoxy-2'-fluoro-                 biphenyl     Example 66  4-bromo-3-fluoro-4'-benzoxy-3'-fluoro-                 biphenyl     Example 67  4-bromo-2-fluoro-4'-benzoxybiphenyl     Example 68  4-bromo-2-fluoro-4'-benzoxy-2',3'-                 difluorobiphenyl     Example 69  4-bromo-2-fluoro-4'-benzoxy-2-fluoro-                 biphenyl     Example 70  4-bromo-2-fluoro-4'-benzoxy-3'-fluoro-                 biphenyl     Example 71  4-bromo-2,3-difluoro-4'-benzoxybiphenyl     Example 72  4-bromo-2,3-difluoro-4'-benzoxy-2',3'-                 difluorobiphenyl     Example 73  4-bromo-2,3-difluoro-4'-benzoxy-2'-                 fluorobiphenyl     Example 74  4-bromo-2,3-difluoro-4'-benzoxy-3'-                 fluorobiphenyl     Example 75  4-bromo-4"-benzoxy-p-terphenyl     Example 76  4-bromo-4"-benzoxy-2",3"-difluoro-p-                 terphenyl     Example 77  4-bromo-4"-benzoxy-2"-fluoro-p-terphenyl     Example 78  4-bromo-4"-benzyloxy-3"-fluoro-p-                 terphenyl     Example 79  4-bromo-4"-benzoxy-2',3'-difluoro-p-                 terphenyl     Example 80  4-bromo-4"-benzoxy-2'-fluoro-p-terphenyl     Example 81  4-bromo-4"-benzoxy-3'-fluoro-p-terphenyl     Example 82  4-bromo-3-fluoro-4"-benzoxy-p-terphenyl     Example 83  4-bromo-3-fluoro-4"-benzoxy-2",3"-                 difluoro-p-terphenyl     Example 84  4-bromo-3-fluoro-4"-benzoxy-2',3'-                 difluoro-p-terphenyl     Example 85  4-bromo-3-fluoro-4"-benzoxy-2',2",3',3"-                 tetrafluoro-p-terphenyl     Example 86  4-bromo-3-fluoro-4"-benzoxy-2',2",3'-                 trifluoro-p-terphenyl     Example 87  4-bromo-3-fluoro-4"-benzoxy-2',2",3"-                 trifluoro-p-terphenyl     Example 88  4-bromo-3-fluoro-4"-benzoxy-2',2"-                 difluoro-p-terphenyl     Example 89  4-bromo-3-fluoro-4"-benzoxy-2',3"-                 difluoro-p-terphenyl     Example 90  4-bromo-3-fluoro-4"-benzoxy-3',3"-                 difluoro-p-terphenyl     Example 91  4-bromo-3-fluoro-4"-benzoxy-3',2"-                 difluoro-p-terphenyl     Example 92  4-bromo-3-fluoro-4"-benzoxy-2'-fluoro-p-                 terphenyl     Example 93  4-bromo-3-fluoro-4"-benzoxy-3'-fluoro-p-                 terphenyl     Example 94  4-bromo-3-fluoro-4"-benzoxy-2"-fluoro-p-                 terphenyl     Example 95  4-bromo-3-fluoro-4"-benzoxy-3"-fluoro-p-                 terphenyl     Example 96  4-bromo-2-fluoro-4"-benzoxy-p-terphenyl     Example 97  4-bromo-2-fluoro-4"-benzoxy-2",3"-                 difluoro-p-terphenyl     Example 98  4-bromo-2-fluoro-4"-benzoxy-2',3'-                 difluoro-p-terphenyl     Example 99  4-bromo-2-fluoro-4"-benzoxy-2',2",3',3"-                 tetrafluoro-p-terphenyl     Example 100 4-bromo-2-fluoro-4"-benzoxy-2',2",3'-                 trifluoro-p-terphenyl     Example 101 4-bromo-2-fluoro-4"-benzoxy-2',2",3"-                 trifluoro-p-terphenyl     Example 102 4-bromo-2-fluoro-4"-benzoxy-2',2"-                 difluoro-p-terphenyl     Example 103 4-bromo-2-fluoro-4"-benzoxy-2',3"-                 difluoro-p-terphenyl     Example 104 4-bromo-2-fluoro-4"-benzoxy-3',3"-                 difluoro-p-terphenyl     Example 105 4-bromo-2-fluoro-4"-benzoxy-3',2"-                 difluoro-p-terphenyl     Example 106 4-bromo-2-fluoro-4"-benzoxy-2"-fluoro-p-                 terphenyl     Example 107 4-bromo-2-fluoro-4"-benzoxy-3'-fluoro-p-                 terphenyl     Example 108 4-bromo-2-fluoro-4"-benzoxy-2"-fluoro-p-                 terphenyl     Example 109 4-bromo-2-fluoro-4"-benzoxy-3"-fluoro-p-                 terphenyl     Example 110 4-bromo-2,3-difluoro-4"-benzoxy-p-                 terphenyl     Example 111 4-bromo-2,3-difluoro-4"-benzoxy-2",3"-                 difluoro-p-terphenyl     Example 112 4-bromo-2,3-difluoro-4"-benzoxy-2',3'-                 difluoro-p-terphenyl     Example 113 4-bromo-2,3-difluoro-4"-benzoxy-                 2',2",3',3"-tetrafluoro-p-terphenyl     Example 114 4-bromo-2,3-difluoro-4"-benzoxy-2',2",3'-                 trifluoro-p-terphenyl     Example 115 4-bromo-2,3-difluoro-4"-benzoxy-2',2",3"-                 trifluoro-p-terphenyl     Example 116 4-bromo-2,3-difluoro-4"-benzoxy-2',2"-                 difluoro-p-terphenyl     Example 117 4-bromo-2,3-difluoro-4"-benzoxy-2',3"-                 difluoro-p-terphenyl     Example 118 4-bromo-2,3-difluoro-4"-benzoxy-3',3"-                 difluoro-p-terphenyl     Example 119 4-bromo-2,3-difluoro-4"-benzoxy-3',2"-                 difluoro-p-terphenyl     Example 120 4-bromo-2,3-difluoro-4"-benzoxy-2'-                 fluoro-p-terphenyl     Example 121 4-bromo-2,3-difluoro-4"-benzoxy-3'-                 fluoro-p-terphenyl     Example 122 4-bromo-2,3-difluoro-4"-benzoxy-2"-                 fluoro-p-terphenyl     Example 123 4-bromo-2,3-difluoro-4"-benzoxy-3"-                 fluoro-p-terphenyl     Example 124 6-bromo-2-(4-benzoxy)phenyl-naphthalene     Example 125 6-bromo-2-(4-benzoxy-2,3-difluoro)phenyl-                 naphthalene     Example 126 6-bromo-2-(4-benzoxy-2-fluoro)phenyl-                 naphthalene     Example 127 6-bromo-2-(4-benzoxy-3-fluoro)phenyl-                 naphthalene     ______________________________________

Example 128 ##STR37## is obtained analogously to Example 1 by coupling of 2,5-dibromopyrimidine and 6-benzoxynaphthalene-2-boronic acid.

Examples 129-131 are obtained analogously:

    ______________________________________     Example 129  5-bromo-2- 6-benzoxynapthalene-2-                  yl!pyridine     Example 130  2-bromo-5- 6-benzoxynapthalene-2-                  yl!pyridine     Example 131  2-bromo-5- 6-benzoxynapthalene-2-yl!-                  pyridine     ______________________________________

Example 132 ##STR38## is obtained analogously to Example 59 by coupling of 2,3-difluorophenylboronic acid and 4-benzoxybromobenzene; as colorless crystals of melting point 82°-83° C.

Examples 133-169 are obtained analogously:

    ______________________________________     Example 133 3-fluoro-4'-benzoxybiphenyl     Example 134 3-fluoro-4'-benzoxy-2',3'-                 difluorobiphenyl     Example 135 3-fluoro-4'-benzoxy-2'-fluorobiphenyl     Example 136 3-fluoro-4'-benzoxy-3'-fluorobiphenyl     Example 137 2,3-difluoro-4'-benzoxybiphenyl     Example 138 2,3-difluoro-4'-benzoxy-2',3'-difluoro-                 biphenyl     Example 139 2,3-difluoro-4'-benzoxy-2'-fluorobiphenyl     Example 140 2,3-difluoro-4'-benzoxy-3-'fluorobiphenyl     Example 141 deleted     Example 142 3-fluoro-4"-benzoxy-p-terphenyl     Example 143 3-fluoro-4"-benzoxy-2",3"-difluoro-p-                 terphenyl     Example 144 3-fluoro-4"-benzoxy-2',3'-difluoro-p-                 terphenyl     Example 145 3-fluoro-4"-benzoxy-2',2",3',3"-                 tetrafluoro-p-terphenyl     Example 146 3-fluoro-4"-benzoxy-2',2",3'-trifluoro-p-                 terphenyl     Example 147 3-fluoro-4"-benzoxy-2',2",3"-trifluoro-p-                 terphenyl     Example 148 3-fluoro-4"-benzoxy-2',2"-difluoro-p-                 terphenyl     Example 149 3-fluoro-4"-benzoxy-2',3"-difluoro-p-                 terphenyl     Example 150 3-fluoro-4"-benzoxy-3',3"-difluoro-p-                 terphenyl     Example 151 3-fluoro-4"-benzoxy-3',2"-difluoro-p-                 terphenyl     Example 152 3-fluoro-4"-benzoxy-2'-fluoro-p-terphenyl     Example 153 3-fluoro-4"-benzoxy-3'-fluoro-p-terphenyl     Example 154 3-fluoro-4"-benzoxy-2"-fluoro-p-terphenyl     Example 155 3-fluoro-4"-benzoxy-3"-fluoro-p-terphenyl     Example 156 2,3-difluoro-4"-benzoxy-p-terphenyl     Example 157 2,3-difluoro-4"-benzoxy-2",3"-difluoro-p-                 terphenyl     Example 158 2,3-difluoro-4"-benzoxy-2',3'-difluoro-p-                 terphenyl     Example 159 2,3-difluoro-4"-benzoxy-2',2",3',3"-                 tetrafluoro-p-terphenyl     Example 160 2,3-difluoro-4"-benzoxy-2',2",3'-                 trifluoro-p-terphenyl     Example 161 2,3-difluoro-4"-benzoxy-2',2",3"-                 trifluoro-p-terphenyl     Example 162 2,3-difluoro-4"-benzoxy-2',2"-difluoro-p-                 terphenyl     Example 163 2,3-difluoro-4"-benzoxy-2',3"-difluoro-p-                 terphenyl     Example 164 2,3-difluoro-4"-benzoxy-3',3"-difluoro-p-                 terphenyl     Example 165 2,3-difluoro-4"-benzoxy-3',2"-difluoro-p-                 terphenyl     Example 166 2,3-difluoro-4"-benzoxy-2'-fluoro-p-                 terphenyl     Example 167 2,3-difluoro-4"-benzoxy-3'-fluoro-p-                 terphenyl     Example 168 2,3-difluoro-4"-benzoxy-2"-fluoro-p-                 terphenyl     Example 169 2,3-difluoro-4"-benzoxy-3"-fluoro-p-                 terphenyl     ______________________________________ 

We claim:
 1. A bifunctional compound of the formula (I), ##STR39## in which: ##STR40## are naphthalene-2,6-diyl or ##STR41## is naphthalene-2,6-diyl or ##STR42## U, X, Y and Z are --CH═, --CF═ and --N═, with the proviso that --CF═ and --N═ may each only be represented at most twice per six-membered ring, and that --CF═ and --N═ may not at the same time be represented twice in a six-membered ring;Hal is Cl, Br or I; or H, if X and/or Y are --CF═l is 0 or 1 m is 0, 1, 2 or
 3. 2. A bifunctional compound as claimed in claim 1, where the symbols in the formula I have the following meanings:l═0 at least one of U, X, Y and Z is --N═ and at most one is --CF═, and the others are --CH═ m is 0, 1 or 2 n is 0, 1 or 2 Hal is Br or I.
 3. A bifunctional compound as claimed in claim 1 or 2, where the symbols in the formula I have the following meanings:l═0 one or two of U, X, Y and Z is --N═, and the others are --CH═ m is 0, 1, 2 or 3 Hal is Br or I.
 4. An intermediate for the preparation of components of liquid-mixtures, of the formula (VI) ##STR43## where the symbols are as defined in the formula (I) in claim 1 and, for the ring carrying the OH function, U and/or Z must be --N═, but X and/or Y must not be --N═.
 5. A process for the preparation of a bifunctional compound of formula (I) ##STR44## in which: ##STR45## are naphthalene-2,6-diyl or ##STR46## is naphthalene-2,6-diyl or ##STR47## U, X, Y and Z are --CH═, --CF═ and --N═, with the proviso that --CF═ and --N═ may each only be represented at most twice per six-membered ring, and that --CF═ and --N═ may not at the same time be represented twice in a six-membered ring;Hal is Cl, Br or I; or H, if X and/or Y are --CF═ R³ is CH₃ or OCH₃ l is 0 or 1 m and n are 0, 1, 2 or 3,which comprises coupling an arylboronic acid of the formula (XXI) ##STR48## in which the substituents and indices have the following meanings: ##STR49## is naphthalene-2,6-diyl or ##STR50## R is CH₃ or OCH₃ m is 0, 1, 2 or 3 n is 0, 1 or 2,with a halogen compound of the formula (XXII) ##STR51## in which Hal is Cl, Br or I and Hal' is Cl, Br, I or perfluoroalkanesulfonate, with catalysis by palladium or a palladium compound, to give a compound of the formula I.
 6. An intermediate for the preparation of components of liquid-crystal mixtures, of the formula (VII) ##STR52## in which ##STR53## is naphthalene-2,6-diyl or ##STR54## X, Y, U and Z are --CH═, --CF═ and --N═, with the proviso that --CH═ and --N═ may each only be represented at most twice per six-membered ring, and that --CF═ and --N═ may not at the same time be represented twice in a six-membered ring and that at least one nitrogen atom must be present in the ring bonded to R⁶ --O--, and that X and/or Y must not be N in this ring,R⁶ is alkyl having 1 to 18 carbon atoms, in which, in addition, one or more non-adjacent --CH₂ -- groups can be replaced by --O--, --CH═CH-- or --Si(CH₃)₂ --, l is 0 or 1 m is 0, 1, 2, or
 3. 7. An intermediate for the preparation of components of liquid-crystal mixtures, of the formula (VIII) ##STR55## in which ##STR56## are naphthalene-2,6-diyl or ##STR57## is naphthalene-2,6-diyl or ##STR58## 1,4-phenylene, optionally substituted once or twice by F, or is 1,4-cyclohexylene or 1,3-dioxane-2,5-diyl;U, X, Y and Z are --CH═, --CF═ and --N═, with the proviso that --CF═ and --N═ may each only be represented at most twice per six-membered ring, and that --CF═ and --N═ may not at the same time be represented twice in a six-membered ring; R⁷ is alkyl having 1 to 18 carbon atoms, in which, in addition, one or more non-adjacent --CH₂ -- groups can be replaced by --O--, --CH═CH-- or --Si (CH₃)--, l is 0 or 1 m is 0, 1, 2 or
 3. 8. An intermediate for the preparation of components of liquid-crystal mixtures, of the formula (XIII), ##STR59## in which the symbols are as defined in the formula (VIII) in claim
 1. 